I pointed out that "even without the financial crisis we would have expected some slowdown in growth this decade (just based on demographics). The good news is that will change soon."

Changes in demographics are an important determinant of economic growth, and although most people focus on the aging of the "baby boomer" generation, the movement of younger cohorts into the prime working age is another key story. Here is a graph of the prime working age population (this is population, not the labor force) from 1948 through February 2016.

Click on graph for larger image.

There was a huge surge in the prime working age population in the '70s, '80s and '90s - and the prime age population has been mostly flat recently (even declined a little).

The prime working age labor force grew even quicker than the population in the '70s and '80s due to the increase in participation of women. In fact, the prime working age labor force was increasing 3%+ per year in the '80s!

So when we compare economic growth to the '70s, '80, or 90's we have to remember this difference in demographics (the '60s saw solid economic growth as near-prime age groups increased sharply).

The prime working age population peaked in 2007, and bottomed at the end of 2012. There are still fewer people in the 25 to 54 age group than in 2007.

The good news is the prime working age group has started to grow again, and is now growing at 0.5% per year - and this should boost economic activity. And it appears the prime working age group will exceed the previous peak later this year.